Web-based resources, such as online information, online retail sites, and other web resources, are widely available to users over networks such as the Internet and intranets. Access to a web resource is provided by a website, which is typically implemented with a server system having one or more servers. Traffic at a popular website can be relatively heavy. If an insufficient number of servers are allocated to a website, then response times experienced by users when visiting the website can be long.
Typically, a server system that provides a website has a multi-tiered architecture that includes multiple tiers of servers. A user request submitted to the server system is typically processed by all the tiers. Thus, the total response time for a user request is the sum of the response times at respective tiers. The expected response time at each tier depends upon the number of servers allocated to the tier.
A web-based, multi-tiered architecture typically includes three tiers of servers: web servers, application servers, and database servers. Web servers communicate with the user (at a client system) and serve as the interface between the application servers and the user. Application servers parse user requests and perform predefined computations. Application servers in turn communicate with database servers to access requested information.
Conventional techniques have been proposed to allocate an adequate number of servers to each tier of a multi-tiered architecture to meet a desired response time constraint. However, conventional techniques for allocating the number of servers in each tier of a multi-tiered architecture employ algorithms that have processing times related exponentially to the input problem size. In other words, as the number of tiers of the multi-tiered server system increases, the processing time for computing the allocation of servers in each tier increases exponentially. Consequently, the amount of processing time involved in performing server allocation using conventional techniques for a multi-tiered server system can be relatively large. Also, conventional techniques are inflexible in that, in a particular system, users typically are limited to using one server allocation algorithm to address the server allocation issue.